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Wurtzite TmAlN (T-m = transition metal) themselves are of interest as semiconductors with tunable band gap, insulating motifs to superconductors, and piezoelectric crystals. Characterization of wurtzite TmAlN is challenging because of the difficulty to synthesize them as single-phase solid solution and such thermodynamic, elastic properties, and high temperature behavior of wurtzite Ti1-xAlxN is unknown. Here, we investigated the high temperature decomposition behavior of wurtzite Ti1-xAlxN films using experimental methods combined with first-principles calculations. We have developed a method to grow single-phase metastable wurtzite Ti1-xAlxN (x = 0.65, 0.75, 085, and 0.95) solid-solution films by cathodic arc deposition using low duty-cycle pulsed substrate-bias voltage. We report the full elasticity tensor for wurtzite Ti1-xAlxN as a function of Al content and predict a phase diagram including a miscibility gap and spinodals for both cubic and wurtzite Ti1-xAlxN. Complementary high-resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950 degrees C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semicoherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1-2 GPa., Funding Agencies|Swedish National Infras-tructure for Computing (SNIC) - Swedish Research Council [VR-2015-04630]; Swedish National Infrastructure for Computing (SNIC); National Academic Infrastructure for Supercomputing in Sweden (NAISS); Swedish Research Council [VR-2015-04630]; VINNOVA (FunMat-II project) [2022-03071]; Swedish Research Council (VR) [2017-03813, 2017-06701, 2021-04426, 2021-00357, 2019-00191]; Swedish government strategic research area [AFM-SFO MatLiU (2009-00971)]; Knut and Alice Wallenberg Foundation [KAW-2018.0194]

Accelerated design of hard-coating materials requires state-of-the-art computational tools, which include data-driven techniques, building databases, and training machine learning models. We develop a heavily automated high-throughput workflow to build a database of industrially relevant hard-coating materials, such as binary and ternary nitrides. We use the high-throughput toolkit to automate the density functional theory calculation workflow. We present results, including elastic constants that are a key parameter determining mechanical properties of hard-coatings, for X1-xYxN ternary nitrides, where X,Y ∈ {Al, Ti, Zr, Hf} and fraction . We also explore ways for machine learning to support and complement the designed databases. We find that the crystal graph convolutional neural network trained on ordered lattices has sufficient accuracy for the disordered nitrides, suggesting that existing databases provide important data for predicting mechanical properties of qualitatively different types of materials, in our case disordered hard-coating alloys., Funding Agencies|Competence Center Functional Nanoscale Materials (FunMat-II) (Vinnova)Vinnova [2016-05156]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation [KAW-2018.0194]; Swedish Government Strategic Research Areas in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Russian Science FoundationRussian Science Foundation (RSF) [18-12-00492]; Swedish Research Council (VR)Swedish Research Council [2020-05402]; Swedish e-Science Centre (SeRC); Swedish Research CouncilSwedish Research CouncilEuropean Commission [2018-05973]

The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)N-y films was investigated. Epitaxial c-(Ti1-xAlx)N-y films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1-xAlx)N-0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1-xAlx)N-y (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1-xAlx)N-y films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 degrees C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)N-y films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd., Funding Agencies|European Unions Erasmus Mundus doctoral program in Materials Science and Engineering (DocMASE)European Union (EU); Swedish Research CouncilSwedish Research Council [2017-03813, 2017-06701]; Swedish government strategic research area grant AFM - SFO MatLiU [2009-00971]; VINNOVA (FunMat-II project)Vinnova [2016-05156]

Ab initio-calculated ideal strength and toughness describe the upper limits for mechanical properties attainable in real systems and can, therefore, be used in selection criteria for materials design. We employ density-functional ab initio molecular dynamics (AIMD) to investigate the mechanical properties of defect-free rocksalt-structure (B1) TiN and B1 Ti1-xAlxN (x = 0.25, 0.5, 0.75) solid solutions subject to [001], [110], and [111] tensile deformation at room temperature. We determine the alloys ideal strength and toughness, elastic responses, and ability to plastically deform up to fracture as a function of the Al content. Overall, TiN exhibits greater ideal moduli of resilience and tensile strengths than (Ti,Al)N solid solutions. Nevertheless, AIMD modeling shows that, irrespective of the strain direction, the binary compound systematically fractures by brittle cleavage at its yield point. The simulations also indicate that Ti0.5Al0.5N and Ti0.25Al0.75N solid solutions are inherently more resistant to fracture and possess much greater toughness than TiN due to the activation of local structural transformations (primarily of B1 -amp;gt; wurtzite type) beyond the elastic-response regime. In sharp contrast, (Ti,Al)N alloys with 25% Al exhibit similar brittleness as TiN. The results of this work are examples of the limitations of elasticity-based criteria for prediction of strength, brittleness, ductility, and toughness in materials able to undergo phase transitions with loading. Comparing present and previous findings, we suggest a general principle for design of hard ceramic solid solutions that are thermodynamically inclined to dissipate extreme mechanical stresses via transformation toughening mechanisms., Funding Agencies|Competence Center Functional Nanoscale Materials (FunMat-II) (Vinnova Grant)Vinnova [2016-05156]; Swedish Research Council (VR)Swedish Research Council [2019-05600]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Knut and AliceWallenberg Foundation throughWallenberg Scholar project [2018.0194]; Olle Engkvist Foundation

Phase, microstructure, and strain evolution during annealing of arc deposited TiZrAlN coatings are studied using in situ x-ray scattering and ex situ transmission electron microscopy. We find that the decomposition route changes from nucleation and growth of wurtzite AlN to spinodal decomposition when the Zr-content is decreased and the Al-content increases. Decomposition of Ti0.31Zr0.24Al0.45N results in homogeneously distributed wurtzite AlN grains in a cubic, dislocation-dense matrix of TiZrN consisting of domains of different chemical composition. The combination of high dislocation density, variation of chemical composition within the cubic grains, and evenly distributed wurtzite AlN grains results in high compressive strains, -1.1%, which are retained after 3 h at 1100 degrees C. In coatings with higher Zr-content, the strains relax during annealing above 900 degrees C due to grain growth and defect annihilation. (C) 2018 Elsevier B.V. All rights reserved., Funding Agencies|VINNOVA (Swedish Governmental Agency for Innovation Systems) [2016-05156]; Swedish Government Strategic Research Area (SFO Mat LiU) [2009 00971]; Swedish Research Council [2017-03813]; Rontgen-Angstrom Cluster frame grants [VR 2011-6505, VR 2017-06701]

The phase stability and mechanical properties of wurtzite (w)-Zr0.25Al0.75N/cubic (c)-TiN and w-Zr0.25Al0.75N/c-ZrN multilayers grown by arc evaporation are studied. Coherent interfaces with an orientation relation of c-TiN (111)[1-10]||w-ZrAlN (0001)[11-20] form between ZrAlN and TiN sublayers during growth of the w-ZrAlN/c-TiN multilayer. During annealing at 1100 °C a c-Ti(Zr)N phase forms at interfaces between ZrAlN and TiN, which reduces the lattice mismatch so that the coherency and the compressive strain are partially retained, resulting in an increased hardness (32 GPa) after annealing. For the w-ZrAlN/c-ZrN multilayer, there is no coherency between sublayers leading to strain relaxation during annealing causing the hardness to drop. The retained coherency between layers and the compressive strain in the w-ZrAlN/c-TiN multilayer results in superior fracture toughness compared to the w-ZrAlN/c-ZrN multilayer as revealed by cross-sectional investigations of damage events under scratch and indentation tests., Preprint